1. Field of the Invention
The present invention relates to a bearing assembly and a rotating anode X-ray tube device employing the bearing assembly.
2. Description of the Prior Art
Ball bearings are well-known for supporting relatively rotating members. Among the variety of devices which utilize ball bearings, the rotating members often become imbalanced because of the structure of the particular device. Sometimes the imbalance is not easily corrected. For instance, as illustrated in FIG. 13, a cylinder 2 is fixed to the outer periphery of a rotary member or shaft 1. A supporting cylinder 3 is partially fitted into the rotary shaft 1. Ball bearings 4 and 5 are interposed between the rotary shaft 1 and the supporting cylinder 3. In this device, rotary shaft 1 is separable from cylinder 2 at a location indicated by the line A--A in the Figure. After providing ball bearings 4 and 5 between rotary shaft 1 and supporting cylinder 3, the location indicated by the line A--A is joined to cylinder 2. In this arrangement, the installation of ball bearings 4 and 5 requires the use of sleeves and nuts. These components, however, tend to cause an imbalanced state in the rotary shaft.
A balancing test is generally performed on an imbalanced rotary member, and in view of the results of the test, it is generally necessary to modify the rotary member or its components in order to correct the imbalance. In the above-described construction, the rotary member has to be temporarily separated at the location shown by the line A--A to correct the imbalance. However, the rotary member is often also imbalanced because of its separation from the cylinder and its subsequent rejoining. Consequently, it is quite difficult and time-consuming to correct an imbalanced condition in a rotary member.
A rotating anode X-ray tube device is a typical device which may be subject to the foregoing imbalance problem. The rotating anode X-ray tube device generally comprises a vacuum envelope, a cathode provided in the vacuum envelope and a rotating anode also provided in the vacuum envelope. The rotating anode is spaced from the cathode. A support member for supporting the rotating anode is provided at one end thereof, and is coaxial with the rotating anode. A cylindrical rotor is supported on the end of the support member opposite the end on which the rotating anode is supported. The rotor comprises a driving motor which cooperates with a stator disposed concentrically with the motor and outwardly of the vacuum envelope, a cylindrical first member disposed inwardly of the rotor, the first member having one end connected to the support member and another end connected to a stationary member, a second member concentric to the first member, and a plurality of ball bearings interposed between the first and second members for providing a relative rotation therebetween. Generally the rotor of the driving motor is positioned close to the stator. Also the rotor is generally cylindrically shaped and light in weight.
In such a rotating anode X-ray tube device, the rotating anode increases in temperature during operation. Therefore, it is necessary to position the ball bearings as far away from the rotating anode as possible to avoid the effects of the increased operating temperatures. Consequently, the ball bearings must be disposed in an internal space of the cylindrical rotor, with the result that the arrangement of the components provided in the vacuum envelope resembles the construction depicted in FIG. 13. With this arrangement, correcting the imbalance of the rotary member is difficult and time consuming.
A typical rotating anode X-ray tube device generally uses ball bearings having balls where an outer surface of each ball is coated with a lubricating film layer of silver, lead or molybdenum disulfide, all of which exhibit a lubricating effect in a vacuum. In the above-described rotating anode X-ray tube device, it is necessary to assemble the rotary member after installing the bearing device. Hence the test of the imbalance of the rotary member and the correction of the imbalance have to be performed in an assembly having ball bearings where the balls are coated with the lubricating film layer. In the above-described rotating anode X-ray tube device, the rotating anode is generally operated at a rotational frequency of approximately 10,000 cycles per minute. The test for imbalance has to be carried out at the same rotational frequency. If this test is done in the above-described assembly, the lubricating film layer on the surface of the ball is damaged or peeled off, resulting in either a reduced life or a decline in reliability of the X-ray tube device, or both.
Thus, a conventional bearing device employing a ball bearing exhibits the following disadvantages. When a conventional bearing device is employed in a rotating anode X-ray tube device, it is difficult and time-consuming to correct the imbalanced condition of the rotary member. Furthermore, particularly where ball bearings are used in a rotating anode X-ray tube device, the lubricating film layer on the surface of each ball is damaged or peeled off when the balancing test and the correction of the imbalance of the rotary member are performed.
Accordingly, it is an object of this invention to provide a rotating anode X-ray tube device capable of performing a balancing test on a rotary member and the correction of an imbalance in the rotary member.
Another object of the present invention is to provide a rotating anode X-ray tube device capable of preventing damage to the bearing which is caused when the balancing test and the correction of the imbalance of the rotary member performed.